1. Field of the Invention
The present invention relates to a variable gain control circuit, and more particularly, to a variable gain control circuit embodied in an integrated circuit device.
2. Description of the Related Art
A variable gain control circuit is used for controlling the amount of transmission output gain depending on distance or other communication environment, particularly when signals are communicated and a wave is emitted or received between mobile communication terminals and base stations. Control of the output gain can improve power efficiency and prevent unnecessary current from being leaked to neighboring channels.
FIG. 1 is a circuit diagram of a conventional variable gain control circuit. Referring to FIG. 1, the conventional variable gain control circuit comprises an input matching unit 111, an analog control circuit 121, an output matching unit 131, bipolar transistors 141˜143 and an inductor 151.
Similar to a difference amplifier, current flows to the bipolar transistor 143 based on the difference of voltages applied to the bases of the bipolar transistors 141, 142. The amount of current which flows to the bipolar transistor 143 is controlled by controlling the size of a control voltage Vc applied to the bases of transistors 141,142 through an analog control circuit 121. When a high frequency signal S1 is input to the bipolar transistor 143 through input matching unit 111, the variable gain control circuit 101 amplifies this signal, and an output signal is generated and output at S2 through the output matching unit 131. The input matching unit 111 impedance matches the input signal S1 and the output matching unit 131 impedance matches circuitry connected to S2.
In the variable gain control circuit 101, an additional analog control circuit 121 is required for more precise linear control. Thus, an integrated circuit device equipped with the variable gain control circuit 101 requires more space, has higher current dissipation and parasitic effects.
Accordingly, a need exists for a variable gain control circuit having a wide range of variable gains without an analog control circuit.